Yes 19mm but the original wheel nuts are of composite construction with thin stainless sheathing for the sake of appearance. They are not a perfect fit and are easily damaged.
I have replaced my wheel nuts with:
FEBI BILSTEIN Wheel Nut
M12 x 1,5mm, 19
Article number: 45789
I bought these for just over £30 for a full set of 20 from Autodoc - German company that provides excellent on-line service with quick delivery. The Febi Bilstein products are solid and precision made whereas my original wheel nuts were all pretty well chewed up. If, like me you regularly change wheels (I use Winter wheels and tyres from November to March) these wheel nuts are a must have!
Yes they are 19mm - and I too replaced all my wheel nuts because I damaged one of the locking wheel nuts - and it was very difficult to remove - and I didn't want the same potential aggro on the remaining three wheels... I bought black nuts to match the wheel inserts.